1. Technical Field
The present invention relates to a resistor-sharing switching circuit.
2. Description of the Related Art
FIG. 1 is a view for exemplifying a general RF switching circuit.
Referring to FIG. 1, switching elements are provided between a transmitting terminal and an antenna and between a receiving terminal and the antenna, and connect the transmitting terminal and the receiving terminal to the antenna alternatively in response to a control signal. Here, a resistor is provided at a control terminal of the switching element in order to allow the control signal to be applied to the control terminal of the switching element.
While a signal transmitted from the transmitting terminal to the antenna and/or a signal transmitted from the antenna to the receiving terminal has a significantly large power, a threshold voltage of a switching element, such as a transistor used in an RF switching circuit, generally has a relatively low power. Therefore, a plurality of transistors are connected in series between the transmitting terminal and/or the receiving terminal and the antenna. When the plurality of transistors are connected in series like this, the number of resistors connected to control terminals of respective transistors is increased.
Meanwhile, when the RF switching circuit is generally realized as a chip, the transistors, which constitute the switching element, and the resistors, which are connected to the control terminals of the transistors, occupy a very large portion in the chip where the RF switching circuit is embodied. For example, in a case of a single-pole-double-throw (SPDT) RF switching circuit, an area occupied by the resistors connected to the control terminals of the switching element reaches about 10% of the total area of the chip.
Recently, in a situation where small size and weight of various kinds of electronic devices are issued, efforts to decrease the size of the chip have continued. However, there is a limit to miniaturize the chip without decreasing the number of transistors and the number of resistors connected to the control terminals of the transistors in the RF switching circuit.